Advances in semiconductor design and fabrication have resulted in ICs with a wide range of functions and performance parameters. Individual analog and mixed signal ICs may be housed in packages having hundreds of pins. In addition to the requirement for testing highly complex individual circuits, parallel testing of multiple ICs with low pin counts also requires a large number of contacts to be made.
In ATE systems, the device(s) being tested are typically mounted on a loadboard that provides a socket for receiving the device(s) under test (DUT) on one side, and a series of contacts on the other side. The printed circuits on the loadboard provide a fixed mapping of the contacts to the pins of the DUT. Each IC design/package type will typically have a dedicated loadboard for testing. Loadboards with characterized loads may also be used for calibration of the ATE.
The contact array of the load board mates to a DUT contactor that has a corresponding array of spring loaded electrical contacts (pogo pins) that provide an electrical connection to the test electronics that can be repeatedly cycled without degradation. The mechanical and electrical requirements of the DUT interface limit the number of pins that may be used in the device contactor, and thus limit the number of available test modules in the ATE at any given time.
The test modules used for analog testing may be divided into two general categories of source and measure, with each category being further divided on the basis of low and high frequency. For testing based upon digital instruments, there is also a division on the basis of resolution that is correlated with frequency. Low frequency testing typically requires greater resolution than high frequency testing, and high resolution is also easier to achieve at lower frequencies.
For example, digital testing of analog audio may require a bandwidth of 0-20 kHz, a signal-to-noise ratio greater than 100 dB, and a resolution of 18-24 bits. Nominally, the low frequency test range is from DC to about 100 kHz or 200 kHz. Low frequency test resolution may be about 18 bits or greater.
High frequency test applications include video circuits for set-top box (STB), and digital versatile disc (DVD), analog-to-digital converters (ADCs), and digital-to-analog-converters (DACs). Other high frequency test requirements include communications circuits such as intermediate frequency (IF) and digital subscriber line (DSL) circuits. The high frequency range is nominally from about 100 kHz or 200 kHz and higher. The resolution for high frequency digital testing is typically less than 18 bits.
Traditionally, each analog resource has required an individual dedicated circuit board. In order to provide source and measurement functions over both low and high frequency ranges, four modules have been required, each with its own set of fixed connections to pogo pins and the control hardware. In the context of the present invention, control hardware is defined as the portion of an ATE system that provides the interface between a human user and a module.
The fixed connections and single function modules of present ATE systems limit the flexibility for testing of analog functions, and also make reconfiguration of the ATE a laborious process. When a different mix of source and measure, or high and low frequency modules is required, modules must be physically removed, replaced, and recabled.
Another difficulty is presented by devices with test requirements of devices that span the boundary between high and low frequency test modules. Due to the tradeoff between resolution and frequency range, it is not uncommon for a broadband device to require testing by both low and high frequency modules.